1. Field of the Invention
The present invention relates to an aeration apparatus and method for producing ultrapure water. More particularly, it pertains to an aeration apparatus and method used in producing ultrapure water in which untreated water is aerated with ozone (O.sub.3), or oxygen (O.sub.2), thereby effecting oxidative destruction of organic matter and converting colloidal substances into solid fine particles that can be removed from the water.
2. Description of the Related Art
FIG. 5 is a schematic view showing a conventional aerating device for producing ultrapure water. Referring to FIG. 5, water to be treated for the oxidative destruction of organic matter and the conversion of colloidal substances into solid fine particles (hereinafter referred to as untreated water) is supplied by an unillustrated pump from a water pipe 5 into a reaction tank 1, which pipe 5 is provided on one lower side of the reaction tank 1. An aeration gas pipe 2 is also provided on the lower side of the reaction tank 1, and extends to the other lower side of the tank 1. The aeration gas pipe 2 is used for feeding an aeration gas, such as ozone (O.sub.3), into the reaction tank 1. Many perforations 3 for injecting the aeration gas into the reaction tank 1 are present in the aeration gas pipe 2. Screens 4a to 4c are located in the reaction tank 1. A discharge pipe 7 is connected to the upper side of the reaction tank 1, and is used for discharging aerated water. The discharge pipe 7, to which a discharge pump 8 is connected, leads to a gas-liquid separation tank 9. A discharge pipe 6 for discharging excessive gas is connected to the ceiling of the reaction tank 1, and means 10 for removing the aeration gas is connected to the exhaust pipe 6.
The conventional aeration apparatus for producing ultrapure water is constructed as described above. The untreated water is fed through the water pipe 5 into the reaction tank 1, where an appropriate amount of untreated water is stored. While the untreated water is being fed, the aeration gas is also fed from the aeration gas pipe 2 and injected through the perforations 3 into the reaction tank 1. The aeration gas is then formed into bubbles which rise in the reaction tank 1.
The term "aeration" refers to the fact that the aeration gas is mixed with and dissolved in the untreated water, whereby the oxidative destruction of organic matter is effected and colloidal substances contained in the water are converted into solid fine particles. Factors, such as the efficiency at which the gas contacts the liquid (gas-liquid contact efficiency) and the solubility of the aeration gas, contribute to the aeration efficiency. Since the diameter of each bubble emerging from the perforations 3 is large, the screens 4a to 4c are provided in order to atomize the bubbles so that the surface area of each bubble increases and the speed at which the bubbles rise decreases, thereby enhancing the gas-liquid contact efficiency.
The fine bubbles of the aeration gas are mixed with and dissolved in the untreated water in the reaction tank 1. Thus, the aeration proceeds. Treated water which has been aerated is drawn by the discharge pump 8, and then led to the gas-liquid separation tank 9 through the discharge pipe 7. The aeration gas dissolved in the treated water is removed in the gas-liquid separation tank 9. The aeration gas which has not been dissolved in the untreated water is discharged through the discharge pipe 6 by the aeration gas removing means 10, such as "AKH2", which is a honeycomb ozone decomposition system manufactured by Kobe Steel Ltd.
In the above-described aeration apparatus for producing ultrapure water, even when the screens 4a to 4c are used, the aeration gas is not formed into sufficiently fine bubbles. In addition, the aeration gas comes into contact with the untreated water only because of the buoyant force of the bubbles. For these reasons, the solubility of the aeration gas in the untreated water is low, thus resulting in poor aeration efficiency. If the time during which the aeration gas is in contact with the untreated water is to be extended in order to enhance the solubility of the gas, the reaction tank has to be large, which entails a higher equipment cost.